1. Field of the Invention
The present invention relates to an image processing apparatus capable of searching for a higher matching accuracy, optimum region on a paper surface at a time when verifying the authenticity of the paper on the basis of a paper fingerprint unique to the paper or the state of the paper surface due to irregular dispersion of toner produced at printing.
2. Description of Related Art
Paper consists of tangles of vegetable fibers of 20 to 30 microns thick. The tangles create a random pattern. The random pattern differs from paper to paper just as a fingerprint. Such a pattern due to unevenness and overlap of random fibers in paper surface is called a paper fingerprint.
In addition, as for a document printed by a printer, copying machine or the like, it is impossible to control up to the minute dispersion of toner particles used for forming an image. Thus, the minute dispersion of the toner becomes irregular. Accordingly, the state of the paper surface due to the irregular dispersion of the toner produced during printing is applicable as unique information formed on the printed paper surface (it is referred to as “print paper surface unique information” hereinbelow).
As described above, on the paper surface, there is a paper fingerprint different from paper to paper regardless of the presence or absence of printing, and the information unique to the printed paper surface created by printing. Accordingly, registering the information on the paper fingerprint different from paper to paper (referred to as “paper fingerprint information” hereinbelow) or the foregoing print paper surface unique information in terms of “the original I have issued is the paper having this paper fingerprint information” makes it possible to distinguish the “original” from a “counterfeit” afterward. The term “counterfeit” naturally includes a “copy of the original”.
Incidentally, claim 6 of Japanese Patent Laid-Open No. 2005-038389 reads as follows.
“The authenticity deciding method characterized by setting to at least one of the reference data and the matching data a gradation value range that is estimated to include a noise component on the basis of gradation value distribution, and by calculating the correlation value after excluding data belonging to the set gradation value range.”
Here, assume that a paper fingerprint information acquiring region or a print paper surface unique information obtaining region is set using the technique of Japanese Patent Laid-Open No. 2005-038389. Then, a pure white region is set as the paper fingerprint information acquiring region or print paper surface unique information obtaining region. However, there is a problem of being unable to make a decision as to whether that region is a region that gives the highest matching rate in the paper surface at a time when verifying the paper fingerprint information or print paper surface unique information.